Foreign women in Malaysia are making extensive use of “husbands for hire” to circumvent immigration laws, according to the country’s immigration director.

The women typically pay the men 5,000 ringgit (about $1500) a month. Many of the women are sex workers, authorities said, and can make four times that much in the same time period, especially if they do not have to leave the country frequently to secure visas.

In past police raids at brothels, foreign prostitutes who produced marriage documents “knew nothing about these so-called husbands and their husbands can’t even recall the names of the wives off-hand,” Immigration Department director-general Datuk Abdul Rahman Othman told the New Straits Times.

Rahman estimated only out of every 25 marriages between a foreign woman and a Malaysian man was legitimate.

Foreign spouses are first given a three-month pass to stay in the country, then a six-month visa. Immigration officials conduct random checks to ascertain that the relationships are real, he said. But the measures have not been enough to stem the tide of fake marriages, especially in Perak, Johor and Penang.